1. Field of the Invention
The present invention relates to a screw spindle assembly of a swivel chair, more particularly to a screw spindle assembly comprised of a clutch which works smoothly so as to give comfort to users; a spindle bushing, which guides an elastic body (i.e. a spring) to move up and down precisely, so as to reduce noise; and a stopper having a same diameter as that of a screw shaft, which are placed on the top of the screw shaft so that a screw nut cannot be detached from the screw shaft.
2. Description of the Related Art
Conventionally, a screw spindle assembly of a swivel chair is located at the bottom of the chair so as to control the height of the chair.
FIG. 1 is an exploded view showing a screw spindle assembly of a conventional swivel chair. FIG. 2 is a cross-sectional view showing the screw spindle assembly of the conventional swivel chair. Reference number 10 is a hollow, cylindrical outer case. Number 20 is the spindle which is mounted in the outer case 10. The spindle 20 includes a tapered end 22 and an inner pipe 24 having a cock which holds a support ring mentioned below.
The spindle 20 encloses an elastic body 30, i.e. a spring, which provides more comfort to users; a ball bearing component which accommodates the smooth revolution of the spindle 20; a rubber ring 60 which maintains the height of the seat; and a screw nut and a clutch 80 which hold the seat at a desirable height.
Reference number 12 is a spindle guide which is placed between the top of the outer case 10 and the top of the spindle 20 and holds them in place. Reference number 32 is a support ring which is placed between the cock 24a and the elastic body 30. Reference numbers 42 and 44 are bearing supports which sandwich and protect the ball bearing component 50, and reference number 52 is a ball bearing found in the ball bearing component 50.
In the spindle, a screw shaft 90 penetrates through the all of the elements which include the elastic body 30, the ball bearing component 50, the rubber ring 60, the screw nut 70 and the clutch 80. The fixer 100, which is comprised of a fixing hole 102 in the shape of a circle, is placed at the bottom of the screw shaft 90 so that the idle-revolution of the screw shaft 90 is prevented.
The screw shaft 90 has a fixing end 92 at the bottom thereof, which corresponds to the fixing hole 102, and a cylindrical nut support 94 is provided in order to prevent the screw nut 70 from coming down completely.
The clutch 80 is attached to the bottom of the spindle 20 by a curling method.
FIG. 5 is a cross-sectional view showing the screw nut 70 and the clutch 80 of the screw spindle assembly of the conventional swivel chair. The screw nut and the clutch are described in detail with reference to FIG. 5. The screw nut 70 includes a tapered mouth 72, into the top of which the rubber ring 60 will be inserted. It also includes a female screw 74 which corresponds to a grooved portion of the screw shaft 90; and grooves 78, which will be engaged with the clutch 80, at the bottom of the screw nut. The clutch 80, which is engaged with the grooves of the screw nut 70 and rotates, includes protruding parts 82 at the top thereof. Each groove 78 of the screw nut 70 is geared with each protruding part 82 of the clutch 80.
FIG. 8 is a cross-sectional view showing a portion of the stoppers 90a, 90b and 90c holding the screw shaft of the screw spindle assembly of the conventional swivel chair. These stoppers 90a, 90b and 90c prevent the screw nut 70 and the clutch 80 from being disassembled.
The stopper 90a is a sill-type which has embossed portions larger than the screwed portions in diameter, the stopper 90b is a cylinder-type to which a cylindrical body is attached, and the stopper 90c is a welding-type in which the furrows and ridges of the screw shaft 90 are welded so that an idle-revolution occurs at that stopper position.
FIG. 10 is a cross-sectional view showing how the screw shaft 90 is fixed to the fixer 100. The fixer 100 supporting the screw shaft 90 is welded to the bottom of the outer case 10. The fixer 100 includes the fixing hole 102 at the center thereof so that the screw shaft 90 is inserted into the fixing hole 102. The lower circumference of the fixing hole and the fixing end 92 which is inserted into the fixing hole are welded as depicted by reference number 98 in FIG. 10 so that the screw shaft 90 is stably attached to the fixer 100. The outer case 10 and the fixer 100 are fixed together by a cocking part 107, and viscid grease is placed between the screw shaft 90 and the screw nut 70 to facilitate smooth movement.
The conventional swivel chair which comprises the spindle screw described above is manufactured by mounting a seat on the top of the spindle screw and placing the bottom of the outer case 10 to the center of the chair-leg.
The height of the chair, i.e. the length between the floor and the seat of the chair, is adjustable. In other words, the height of the chair is controlled by rotating the seat clockwise and counter-clockwise. In accordance with the rotation of the seat, the spindle 20 which is connected to the seat rotates, and the clutch 80 also rotates because the clutch 80 is attached to the bottom of the spindle 20 via cocking.
The clutch 80 is engaged with the screw nut 70 so that the screw nut 70 moves up and down in relation to the screw shaft 90. In other words, the rotation of the spindle 20 is converted to the vertical motion of the rotating spindle so that the seat moves up and down in accordance with the vertical motion of the rotating spindle 20 because the screw shaft 90 is attached to the outer case 10 by the fixer 100.
When some weight is applied to the spindle 20, i.e. when a user sits on the chair, the spindle 20 moves down and clutch 80 detaches from the nut 70. When no weight is applied to the spindle 20, i.e. when the chair is not being used, the spindle 20 moves up and the clutch 80 attaches to the nut 70. Therefore, the height of the chair is controlled by engaging the clutch 80 with the nut 70.
The conventional swivel chair described above has the following problems.
1. The cross sectional shapes of furrows 78 and ridges 82 of the nut 70 and the clutch 80 are rectangular (see FIG. 5). When the nut 70 and the clutch 80 are precisely engaged, neither shock nor noise occur. However, when the nut 70 and the clutch 80 are not precisely engaged, i.e. furrows of the clutch 80 and the nut 70 meet unintentionally, the clutch 80 and the nut 70 are re-engaged by the elastic body 30, and shock and noise occur. A user, as a result, feels more discomfort.
2. When some weight is applied to the seat, the elastic body 30 is compressed, and moves down causing friction between it and other components around it. In other words, the elastic body 30 rubs against the thread of the screw shaft 90 and the spindle 20, and noise such as a grinding metal sound occurs. When the elastic body 30 is de-compressed and moves up, the noise reoccurs.
3. Stoppers 90a, 90b and 90c of the conventional screw spindle assembly have the following problems. First, the sill-type stopper 90a has a larger diameter than the screw of the screw shaft 90. This stopper makes noise when it contacts the elastic body 30 as the elastic body moves up and down. Further, when components such as ball bearing component 50 require repair or replacement, the spindle screw having this stopper can not be disassembled. Therefore, a new spindle screw must replace the old one, increasing the cost for repairing the spindle 20. Secondly, the cylinder-type stopper 90b and the welding-type stopper 90c cannot be disassembled from the spindle. Therefore, a new screw spindle assembly is also required to replace the old one when repair or replacement is required, again, increasing the cost for repairing the spindle 20.
4. The fixing end 92 of the screw shaft 90 is welded to the fixer 100 which results in a more complicated manufacturing process and in decreased efficiency. In order to weld the fixing end to the fixer vertically, an expert welder is required. As a result of the welding, a pleasing aesthetic appearance cannot be obtained due to the welded portion. Furthermore this welding requirement makes for a more disorganized work environment.
In addition, it is not easy to form the fixing hole 102 in the fixer 100.